1. Field of the Invention
The present invention relates generally to microprogram controllers, and more particularly, to microprogram controllers in information processors which control readout of a microprogram stored in a plurality of storages.
2. Description of the Related Art
In recent years, conventional microprogram-controlled information processors tend to use larger-sized microprograms in order to increase their performance. On the other hand, improvement in performance of an information processor requires reduction of the number of necessary machine cycles and manufacturing costs etc. It is therefore undesirable to highly increase a capacity of an internal control storage for storing a microprogram of an information processor.
To avoid a further increase in a capacity of a storage, overlay microprogram systems have been proposed. In an overlay microprogram control system, a microprogram, which is too large in size to be held in an internal control storage provided in an information processor, is stored in an external storage with a large capacity. The microprogram is divided into a plurality of blocks, loaded on a block basis from the external storage into the internal control storage in the information processor, and then executed by the control storage in the information processor after the loading.
However, with an extremely long microprogram to be loaded into a control storage in an information processor from an external control storage, the above-described conventional overlay microprogram control system requires repetitions of loading of the microprogram because it is divided into blocks. As a result, not only a loading time but also a time for controlling loading are increased, making an overall processing time longer and thereby degrading the performance of the information processor.